This invention relates to an arrangement for an automatic clutch for use in connection with a manually shifted transmission for selectively connecting the output shaft of the vehicle engine to the input shaft of the transmission.
More particularly, the invention relates to a clutch actuation arrangement having a clutch actuating servo motor operated by auxiliary power (pneumatic for example) and having a control device or means for controlling the servo motor as a function of the position of the accelerator pedal and/or the speeds measured at the input to the clutch (engine speed) and at the output of the clutch (transmission input speed).
Automatic automobile clutches have been known in the prior art and usually make use of a pneumatic servo motor. The motor is usually arranged to provide disengagement of the clutch through vacuum pressure action on the servo motor. Engagement of the clutch, on the other hand, is usually effected through venting of the servo motor and must be effected as smoothly as possible to avoid undesirable shocks and jerks in the vehicle motion as the clutch is engaged.
An arrangement providing for smooth engagement of the clutch is described in detail, for example, in the commonly owned, co-pending U.S. patent application Serial No. 165,686 filed July 3, 1980 corresponding to German patent application No. P 29 27 175.8 filed July 5, 1979, and now U.S. Pat. No. 4,331,226, comprising a pneumatic control motor which is responsive to signals received from control valves in accordance with the position of the accelerator pedal and/or the rotational speed of the engine shaft and transmission shaft measured on opposite sides of the clutch. The disclosure of that U.S. application is incorporated herein by reference. That application discloses the operation of clutch engagement where the engine is running and the vehicle is at a standstill. The starting of the vehicle is controlled so that the engine rotational speed is brought to a prescribed value by means of engagement or disengagement of the clutch, the prescribed value being variable as a function of the accelerator pedal position. Control is thereby effected step by step by a plurality of control pulses occurring at time intervals. By modifying the pulse length or pulse frequency, a control device influences the progress of clutch control. The operation of such a control device is described in detail in the commonly owned co-pending U.S. patent application Ser. No. 123,440, filed Feb. 21, 1980, and now U.S. Pat. No. 4,343,387, corresponding to German patent application No. P 29 06 587.0 filed Feb. 21, 1979. The disclosure of that U.S. application is incorporated herein by reference. There, a control pulse is varied as a function of the difference between the actual engine rotational speed and the desired engine rotational speed so that as the difference between the actual and desired rotational speed increases, the pulse increases either linearly or progressively. In other words, the more the engine speed differs from the desired speed, the more the engine speed is caused to approximate the desired speed by actuation of the clutch.
In the above-described arrangement of U.S. application Ser. No. 165,687 it is assumed that the clutch engagement process is accomplished through venting of the servo motor by connection of the servo motor to the atmosphere by one of the control valves. Conversely, the disengagement process is accomplished by connection of the servo motor with vacuum storage by the other control valve.
It is known that automobile clutches operating with friction linings, as is customary, must overcome a relatively long period of free travel of the clutch before the friction linings begin to take hold. The above-described co-pending application Ser. No. 165,687 overcomes this deficiency by effecting clutch engagement by a series of pulses succeeding each other at time intervals.
Because it is desirable, however, to overcome this period of free travel of the clutch as rapidly as possible, the present invention is an improvement over the co-pending application because it substitutes for this series of pulses, an initial pulse of sufficient duration to almost completely overcome the free travel of the clutch.